Multi-layer circuit board

ABSTRACT

A multi-layer circuit board includes a plurality of circuit substrates, a plurality of dielectric layers, and a plurality of metal bumps. Each circuit substrate includes two first trace layers and an insulating layer between the two trace layers. Each electric layer is laminated between two neighboring circuit substrates. At latest one metal bump is arranged between each two neighboring circuit substrates. Each metal bump passes through one dielectric layer. Two opposite ends of each metal bump are connected with the trace layer of the circuit substrate to be electrically connected to the two neighbor circuit substrates.

This application is a divisional application of a commonly-assigned application entitled “MULTI-LAYER CIRCUIT BOARD AND METHOD FOR MANUFACTURING SAME”, filed on Jun. 24, 2013 with application Ser. No. 13/925136. The disclosure of the above-identified application is incorporated herein by reference.

FIELD

The present disclosure generally relates to circuit board technology, and particularly to a multi-layer circuit board and method for manufacturing the multi-layer circuit board.

BACKGROUND

To accommodate the development of miniaturized electronic products with multiple functions, multilayer printed circuit boards are widely used due to their characteristics such as lightness and high-density interconnectability.

Multilayer printed circuit boards are manufactured by using a typical sheet-by-sheet process. First a core substrate is provided, and an inner electrically conductive trace layer is formed on the core substrate. Second, an adhesive layer and a first electrically conductive layer such as a copper foil are sequentially laminated onto the core substrate. Third, a blind hole is formed in the adhesive layer and the first electrically conductive layer. Fourth, a first electrically conductive trace layer is formed by selectively etching the first electrically conductive layer, and a plated metal layer is formed in the blind hole to form a blind via, thus the first electrically conductive trace layer electrically communicates to the inner electrically conductive trace layer by the blind via. Afterwards, another adhesive layer and a second electrically conductive layer are sequentially laminated onto the first electrically conductive trace layer, another electrically conductive trace layer is formed by selectively etching the second electrically conductive layer, and another blind via is formed to electrically communicates the second electrically conductive layer and the first electrically conductive layer. Thus, a multilayer printed circuit board is obtained. However, only one electrically conductive layer can be laminated at one time. Thus, the process for making the multilayer printed circuit board is too long, and a cost for manufacturing the multilayer printed circuit board is too high.

What is needed, therefore, is a multi-layer circuit board and method for manufacturing the multi-layer circuit board to overcome the above-described problems.

BRIEF DESCRIPTION OF THE DRAWINGS

Implementations of the present technology will now be described, by way of example only, with reference to the attached figures.

FIG. 1 is a schematic, cross-sectional view of a copper clad laminate according to a first embodiment.

FIG. 2 is similar to FIG. 1, but showing a through hole defined in the copper clad laminate.

FIG. 3 is similar to FIG. 2, but showing a f plated through hole formed in the copper clad laminate.

FIG. 4 is similar to FIG. 3, but showing a first trace layer and a second trace layer formed in the copper clad laminate to form a first circuit substrate.

FIG. 5 is similar to FIG. 4, but showing a dielectric layer laminated on the first circuit substrate to form a second circuit substrate.

FIG. 6 is similar to FIG. 4, but showing a photo resist layer attached on each surface of the first circuit substrate.

FIG. 7 is similar to FIG. 6, but showing a through hole defined in each photo resist layer.

FIG. 8 is similar to FIG. 7, but showing a copper layer formed in the through hole defined in each resist.

FIG. 9 is similar to FIG. 8, but showing a tin layer formed on the copper layer in the through hole of the photo resist layer.

FIG. 10 is similar to FIG. 9, but showing the photo resist layer removed to obtain a third circuit board.

FIG. 11 is similar to FIG. 10, but showing a third circuit board laminated between two second circuit boards to obtain a multi-layer circuit board.

FIG. 12 is similar to FIG. 11, but showing a solder mask formed on the surface of the multi-layer circuit board according to the first embodiment.

FIG. 13 is a schematic, cross-sectional view of a copper clad laminate according to a second embodiment.

FIG. 14 is similar to FIG. 13, but showing a first trace layer and a second trace layer formed in the copper clad laminate to obtain a first circuit substrate.

FIG. 15 is similar to FIG. 14, but showing a dielectric layer laminated on a surface of the first circuit substrate to form a second circuit substrate.

FIG. 16 is similar to FIG. 14, but showing each dielectric layer laminated on each opposite surface of the first circuit substrate to form a fourth circuit substrate.

FIG. 17 is similar to FIG. 14, but showing a metal bump formed on the first circuit substrate to obtain a third circuit substrate.

FIG. 18 is similar to FIG. 17, but showing two second circuit substrates, two third circuit substrates and one fourth circuit substrate laminated to obtained a multi-layer circuit board according to the second embodiment.

FIG. 19 is similar to FIG. 18, but showing a solder mask formed on the surface of the multi-layer circuit board.

DETAILED DESCRIPTION

It will be appreciated that for simplicity and clarity of illustration, where appropriate, reference numerals have been repeated among the different figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order to provide a thorough understanding of the embodiments described herein. However, it will be understood by those of ordinary skill in the art that the embodiments described herein can be practiced without these specific details. In other instances, methods, procedures, and components have not been described in detail so as not to obscure the related relevant feature being described. Also, the description is not to be considered as limiting the scope of the embodiments described herein. The drawings are not necessarily to scale and the proportions of certain parts have been exaggerated to better illustrate details and features of the present disclosure.

Several definitions that apply throughout this disclosure will now be presented.

The term “comprising,” when utilized, means “including, but not necessarily limited to”; it specifically indicates open-ended inclusion or membership in the so-described combination, group, series and the like.

The present disclosure is described in relation to a multi-layer circuit board. The multi-layer circuit board comprises a plurality of circuit substrates, a plurality of dielectric layers, and a plurality of metal bumps. Each circuit substrate comprises two first trace layers and an insulating layer between the two trace layers. Each electric layer is laminated between two neighboring circuit substrates. At latest one metal bump is arranged between each two neighboring circuit substrates. Each metal bump passes through one dielectric layer. Two opposite ends of each metal bump are connected with the trace layer of the circuit substrate to be electrically connected to the two neighbor circuit substrates.

A method of manufacturing a multi-layer circuit board according to a first embodiment includes the steps as follows.

FIG. 1 shows in step 1, three copper clad laminates 110 are provided. Each copper clad laminate 110 includes a first copper layer 111, an insulating layer 112 and a second copper layer 113 stacked in above descried order. The copper clad laminate 110 may be a flexible copper clad laminate or a rigid copper clad laminate.

FIGS. 2, 3 and 4 show in step 2, a plated through hole 114 is formed in each copper clad laminate 110. A first trace layer 115 is formed by selectively removing portions of first copper layer 111. A second trace layer 116 is formed by selectively removing portions of second copper layer 113. The first trace layer 115 and the second trace layer 116 electrically communicate via the plated through hole 114, thus, three first circuit substrates 10 are obtained.

In the present embodiment, the plated through hole 114 may be formed by the following steps. First, a through hole 1101 is defined in the copper clad laminate 110. The through hole 1101 runs through the first copper layer 111, the insulating layer 112 and the second copper layer 113. The through hole 1101 may be formed by laser. Second, the through hole 1101 is filled by plated metal to obtain a plated through hole 114.

FIG. 5 shows in step 3, each dielectric layer 40 is laminated on first trace layer 115 of two of the three first circuit substrates 10, thus two second circuit substrate 20 are obtained.

In the present embodiment, the dielectric layer 40 is made of Ajinomoto build-up film (ABF). The dielectric layer 40 may be laminated on the first trace layer 115 by a vacuum laminator. After laminating, the dielectric layer 40 is in B-stage. In other words, the dielectric layer 40 will soften and able to float under high temperature and high pressure, and then will be cured. It can be understood, the dielectric layer 40 also can be made from other dielectric material, such as polyimide (PI).

FIGS. 6, 7, 8 and 9 show step 4, a first metal bump 1151 is formed on the first trace layer 115 and a second metal bump 1161 is formed on the second trace layer 116 of the other one of the three first circuit substrate 10, thus a third circuit substrate 30 is obtained.

In the present embodiment, the first metal bump 1151 and the second metal bump 1161 may be formed by the following steps.

First, as FIG. 6 shows, a first photo resist layer 117 and a second photo resist layer 118 are formed on two opposite surfaces of the first circuit substrate 10. The first photo resist layer 117 and the second trace layer 118 may be made of photo resist. The first photo resist layer 117 and the second photo resist layer 118 may be formed by printing liquid photo resist or laminating a dry film. A thickness of the first photo resist layer 117 or the second photo resist layer 118 may be equal to that of the dielectric layer 40.

Second, as FIG. 7 shows, a first hole 1171 is defined in the first photo resist layer 117, and a second hole 1181 is defined in the second photo resist layer 118. The first hole 1171 and the second hole 1181 may be formed by laser. Portion of the first trace layer 115 is exposed form the first hole 1171. Portion of the second trace layer 116 is exposed from the second hole 1181.

Third, as FIGS. 8 and 9 show, a first metal bump 1151 is formed in the first hole 1171, and a second metal bump 1161 is formed in the second hole 1181. The first metal bump 1151 is composed of a first copper layer 1152 and a first tin layer 1153. The first copper layer 1152 may be formed by electrical plated copper on the surface of the first trace layer 115 exposed in the first hole 1171. A thickness of the first copper layer 1152 is smaller than that deepness of the first hole 1171. The first tin layer 1153 may be formed by electrical plating tin on the surface of the first copper layer 1152 exposed in the first hole 1171. The second metal bump 1161 is composed of a second copper layer 1162 and a second tin layer 1163. The second copper layer 1162 may be formed by electrical plated copper on the surface of the second trace layer 116 exposed in the second hole 1181. A thickness of the second copper layer 1162 is smaller than that deepness of the second hole 1181. The second tin layer 1163 may be formed by electrical plated tin on the surface of the second copper layer 1162 exposed in the second hole 1181.

Fourth, as FIG. 10 shows, the first photo resist layer 117 and the second photo resist layer 118 are removed.

FIG. 11 shows in step 5, the third circuit substrate 30 is stacked and laminated between two second circuit substrates 20, and the dielectric layers 40 of the second circuit substrates 20 is adjacent to the third circuit substrate 30, the first metal bump 1151 and the second metal bump 1161 pass through the dielectric layers 40 adjacent and electrically connect to the first trace layers 115 of the second circuit substrates 20, respectively.

In detail, before laminating, the dielectric layers 40 are in B-stage. When laminating, the dielectric layers 40 become soften and able to float, thereby, the first metal bump 1151 and the second metal bump 1161 can pass through the dielectric layers 40 and connect to the first trace layers 115 of the second circuit substrates 20.

In step 6, the first tin layer 1153 and the second tin layer 1163 are bond with the first trace layers 115 using a reflow soldering process.

In present embodiment, the laminated third circuit board 30 and two second circuit substrates 20 is positioned in a reflow oven to bake. A peak baking temperature is in a range from 210° C. to 230° C. When baking, the first tin layer 1153 and the second tin layer 1163 are melted and bond with the first trace layer 115.

In step 7, the dielectric layers 40 are cured by post baking, and a multi-layer circuit board 100 is obtained as FIG. 11 shows.

In the post baking, the baking temperature is in a range from 100° C. to 15° C. The post baking last time is in a range from 30 minutes to 90 minutes.

As FIG. 12 shows, the method may further includes forming a solder mask 101 on surfaces of the multi-layer circuit board 100 to protect the second trace layer 116.

As FIGS. 11 and 12 show, the multi-layer circuit board 100 includes two second circuit substrates 20 and one third circuit substrate 30. The third circuit substrate 30 is sandwiched between the two second circuit substrates 20.

In other words, the multi-layer circuit board 100 includes three first circuit substrates 10 and two dielectric layers 40. Each dielectric layer 40 is arranged between two neighbor first circuit substrates 10. The metal pump 1151 or 1161 is arranged in each dielectric layer 40 and passes through each dielectric layer 40. Two neighbor first circuit substrates 10 are electrically connected with each other via the metal pump 1151 or 1161 therebetween. The dielectric layer 40 is made of ABF. The first metal bump 1151 is composed of a first copper layer 1152 and a first tin layer 1153. The second metal bump 1161 is composed of a second copper layer 1162 and a second tin layer 1163.

A method of manufacturing a multi-layer circuit board according to a second embodiment includes the steps as follows.

FIG. 13 shows in step 1, five copper clad laminates 210 are provided. Each copper clad laminate 210 includes a first copper layer 211, an insulating layer 212 and a second copper layer 213 stacked in above described order. The copper clad laminate 210 may be a flexible copper clad laminate or a rigid copper clad laminate.

FIG. 15 shows in step 2, a plated through hole 214 is formed in each copper clad laminate 210. A first trace layer 215 is formed by selectively removing portions of first copper layer 211. A second trace layer 216 is formed by selectively removing portions of second copper layer 213. The first trace layer 215 and the second trace layer 216 electrically communicate via the plated through hole 214. Thus, five first circuit substrates 50 are obtained.

In the present embodiment, the plated through hole 214 may be formed by the following steps. First, a through hole is defined in the copper clad laminate 210. The through hole passes through the first copper layer 211, the insulating layer 212 and the second copper layer 213. The through hole may be formed by laser. Second, the through hole is filled by plated metal to obtain the plated through hole 214.

FIGS. 15 and 16 show step 3, in which three first circuit boards are chosen from the five first circuit substrates 50. Two dielectric layers 60 are respectively laminated on the first trace layers 215 of two chosen first circuit substrates 50, thus two second circuit substrate 70 are obtained. Another two dielectric layers 60 are respectively laminated on the first trace layer 215 and the second trace layer 216 of the other chosen first circuit substrate 50 thus a fourth circuit substrate 80 is obtained.

In the present embodiment, the dielectric layer 60 is made of ABF. The dielectric layer 60 may be laminated on the first trace layer 215 by a vacuum laminator. After laminating, the dielectric layer 60 is in B-stage. In other words, the dielectric layer 60 will soften and able to float under high temperature and high pressure, and then will be cured.

FIGS. 17 shows in step 4, each first metal bump 2151 is respectively formed on the first trace layer 215 of the remaining two of the five first circuit boards 50, each second metal bump 2161 is respectively formed on the second trace layer 216 of the remaining two of the five first circuit boards 50. Accordingly, two third circuit substrates 90 are obtained.

In the present embodiment, the first metal bump 2151 and the second metal bunp 2161 may be formed by the same method as the first metal bump 1151 and the second metal bump 1161 in the first embodiment.

The first metal bump 2151 is composed of a first copper layer 2152 and a first tin layer 2153. The second metal bump 2161 is composed of a second copper layer 2162 and a second tin layer 2163.

FIG. 18 shows in step 5, the two third circuit board 30 are arranged between two second circuit substrates 20, the fourth circuit board 80 is arranged between the two second circuit substrates 70, and the dielectric layer 60 of each second circuit substrates 70 is adjacent to neighboring the third circuit substrate 90. Then, the two second circuit substrates 70, the two third circuit substrates 90 and the fourth circuit substrate 80 are laminated. The first metal bump 2151 and the second metal bump 2161 respectively pass through the dielectric layers 60 adjacent and electrically connect to the first trace layers 215 of the second circuit substrates 20, the first trace layer 215 or second trace layer 216 of the fourth circuit substrate 80.

In detail, before laminating, the dielectric layers 60 are in B-stage. When laminating, the dielectric layers 60 become soften and able to float, thus, the first metal bump 2151 and the second metal bump 2161 can pass through the dielectric layers 20 and connect to the first trace layers 215 of the second circuit substrates 20, the first trace layer 215 or second trace layer 216 of the fourth circuit substrate 80.

In step 6, the first tin layer 2153 and the second tin layer 2163 are respectively bond with the first trace layers 215 of the second circuit substrates 20, the first trace layer 215 and the second trace layer 216 of the fourth circuit substrate 80 using a reflow soldering process.

In present embodiment, the laminated the two second circuit substrates 70, the two third circuit substrates 90 and the fourth circuit substrate 80 are positioned in a reflow oven to bake. A peak baking temperature is in a range from 210° C. to 230° C. When baking, the first tin layer 2153 and the second tin layer 2163 are melted and bond with the first trace layers 215 of the second circuit substrates 20, the first trace layer 215 and the second trace layer 216 of the fourth circuit substrate 80.

In step 7, the dielectric layers 60 are cured by post baking, and a multi-layer circuit board 200 is obtained.

In the post baking, the baking temperature is in a range from 100° C. to 15° C. The post baking last time is in a range from 30 minutes to 90 minutes.

As FIG. 19 shows, the method may further includes forming a solder mask 201 on surfaces of the multi-layer circuit board 200.

It can be understood, the present method for manufacturing multi-layer circuit board also can applying for manufacturing more layers circuit board. If N+1 third circuit substrates 90, N fourth circuit substrates 80 and two second circuit substrates 80 are provided, wherein N is a natural number and not less than 1, the N+1 third circuit substrates 90 and the N fourth circuit substrates 80 are arranged between the two second circuit substrates 70, only one fourth circuit substrate 80 is arranged between two neighbor third circuit substrates 90, and only one third circuit substrate 90 is arranged between two neighbor two fourth circuit substrates 80. Then, the N+1 third circuit substrates 90, N fourth circuit substrates 80 and two second circuit substrates 80 are laminated and processed as in step 6 and 7, thus a 4N+6 layers circuit board will be obtained.

In other words, the multi-layer circuit board 200 includes 2N+3 first circuit substrates 50, 2N+2 dielectric layers 60, and a number of first and second metal bumps 2151, 2161. Each dielectric layer 60 is laminated between two first circuit substrates 50. At least one first mental bump 2151 or at least one second mental bump 2161 is arranged between two first circuit substrates 50. Each first metal bump 2151 or second metal bump 2161 passes through one dielectric layer 60. Each two opposite ends of the first metal bump 2151 or second metal bump 2161 connects with first trace layer 215 and second trace layer 216 of the first circuit substrate 50 to electrically communicating the two neighbor first circuit substrates 20.

In the present embodiment, in the process of manufacturing the multi-layer circuit board, only one time laminating process is needed. Accordingly, the time of manufacturing the multi-layer circuit board can be reduced. In addition, the circuit substrates are formed respectively, the rate of finished product of multi-layer circuit board is higher.

Particular embodiments are shown and described by way of illustration only. The principles and the features of the present disclosure may be employed in various and numerous embodiments thereof without departing from the scope of the disclosure as claimed. The above-described embodiments illustrate the scope of the disclosure but do not restrict the scope of the disclosure. 

What is claimed is:
 1. A multi-layer circuit board comprising: a plurality of circuit substrates, each of the plurality of circuit substrates comprising two first trace layers and an insulating layer between the two trace layers; a plurality of dielectric layers, each of the plurality of dielectric layers being laminated between two neighboring circuit substrates; and a plurality of metal bumps, at latest one of the plurality of metal bumps being arranged between two neighboring circuit substrates of the plurality of circuit substrates, each metal bump passing through one dielectric layer, two opposite ends of each metal bump connected with the trace layer of the circuit substrate to be electrically connected to the two neighbor circuit substrates.
 2. The multi-layer circuit board of claim 1, wherein each of the plurality of the metal bump comprises a copper layer and a tin layer, and the tin layer is connected with the trace layer of the adjacent circuit substrate.
 3. The multi-layer circuit board of claim 1, wherein each of the plurality of the dielectric layer is composed of an Ajinomoto build-up film. 